Schemes of supplying fuel from a fuel tank to an intake system of an internal combustion engine includes a scheme of supplying fuel by using a fuel pump and a scheme of supplying fuel by using the gravity. According to the scheme of supplying fuel by using the gravity, a fuel tank is disposed above a carburetor and the fuel is supplied from the fuel tank to the carburetor. This scheme employs a relatively simple configuration and is often used.
According to the scheme of supplying fuel by using the gravity, an automatic cock is disposed in a fuel supply path to introduce the fuel from the fuel tank to the carburetor. The automatic cock is a valve that opens the fuel supply path by using a negative pressure in a crankcase. During the driving of the internal combustion engine, a negative pressure is generated in the crankcase associated with the reciprocating motion of a piston (more specifically, a large negative pressure and a micro positive pressure are alternately and repeatedly generated). The automatic cock is opened by this negative pressure and, thereby, the fuel in the fuel tank flows into the carburetor through the fuel supply path.
A common internal combustion engine rakes up a lubricating oil stored in the crankcase upward to splash the lubricating oil and, thereby, generates oil mist to lubricate a portion to be slid that is accommodated in the crankcase. This is not preferable because the oil mist adheres to parts in the automatic cock when the oil mist intrudes into the automatic cock.
In contrast, a fuel supplying apparatus that suppresses intrusion of the oil mist into a negative pressure introducing inlet of the automatic cock is known from, for example, Japanese Patent No. 4310294. In the known fuel supplying apparatus: a crankcase is connected to an intake system through a gas/liquid separating apparatus, a breather path, and a reed valve; and a branch outlet that branches from the breather path is connected to the negative pressure introducing inlet of the automatic cock.
When a positive pressure is generated in the crankcase, the reed valve is opened by the positive pressure. Oil mist and blowby gas produced in the crankcase are caused to circulate from the crankcase to the intake system and, thereby, are combusted in a combustion chamber. On the other hand, when a negative pressure is generated in the crankcase, the automatic cock is opened by this negative pressure. The fuel in the fuel tank is supplied to the carburetor through the fuel supply path.
The gas/liquid separating apparatus is positioned between the crankcase and the breather path, and separates from the air the oil mist produced in the crankcase. Therefore, the intrusion is suppressed of the oil mist into the negative pressure introducing inlet of the automatic cock through the breather path. In addition, the automatic cock is positioned immediately and exactly above the crankcase. Therefore, even if the oil mist intrudes into the negative pressure introducing inlet of the automatic cock, the oil mist tends to flow out to the breather path thereunder due to the gravity.
When the automatic cock is disposed immediately and exactly above the crankcase adjacent thereto, the thermal influence needs to be fully taken into consideration that is caused by the heat dissipation of the internal combustion engine. When the automatic cock is disposed above the crankcase far away therefrom to avoid receiving the thermal influence, the degree of freedom of disposing the fuel supplying apparatus is reduced and, therefore, this is not preferable. In addition, the fuel supplying apparatus employs the scheme of supplying the fuel by using the gravity and, therefore, the fuel tank is positioned above the automatic cock. Especially, for a configuration that has an internal combustion engine and a fuel supplying apparatus incorporated as one unit such as, for example, a small sound-proof engine-driven generator, the height of the unit as a whole is often limited. To suppress the total height, it is considered to make the fuel tank thin. However, this result in reducing the capacity of the fuel tank and, therefore, this is not an advisable solution.